The present invention relates to a process for producing a monocrystalline layer on an insulator and, more particularly, for growing a monocrystalline layer by locally annealing for a short time a nonmonocrystalline layer formed on an insulator on a semiconductor wafer.
Considerable research has been performed with the goal of producing a monocrystalline layer of silicon on an insulator, and particularly for producing three-dimensional large-scale integrated circuits (LSI's). A silicon wafer for such use generally accommodates three-dimensional LSI's in the bulk of the wafer.
In the prior art, the silicon wafer is mounted on a carbon plate heater to heat the entire bulk of the wafer by conduction to about 1,200.degree. C. At the same time, a carbon strip heater moves over the silicon wafer to anneal by heat radiation a local region of the wafer at about 1,420.degree. C., the melting point of silicon. The beam of heat from the carbon strip heater melts the local region so as to transform the polycrystalline silicon to monocrystalline silicon. Semiconductor elements can then be formed on the silicon monocrystalline layer. The overall heating and local annealing of the wafer, of course, are conducted in an inert atmosphere so as to reduce oxidation and evaporation of the carbon.
This prior art, however, has the drawback that the protracted heating of the overall wafer at 1,200.degree. C. causes rediffusion of the impurity previously implanted in the wafer. This in turn leads to deteriorated performance of the produced LSI's.
S. Iwamatsu discloses, in Japanese Unexamined Patent Publication (Kokai) No. 56-80138, using a rod-like heat source, such as a xenon lamp provided with a reflective mirror, to scan an energy beam having a linear section over a semiconductor wafer or a layer deposited thereon. From our experience, however, it is substantially impossible for a single commercially available lamp to melt a portion of a semiconductor wafer and transform a nonmonocrystalline layer of silicon to a monocrystalline layer due to its low emitting power, even if the beam is focused thereon.
M. Haond et al disclose, in Electronics Letters, Aug. 19, 1982, vol. 18, No. 17, using a plurality of low-power halogen lamps to preheat a wafer from the back side to a temperature of 300.degree. C. to 1100.degree. C. and using a beam focused on the front surface to supply the additional amount of energy necessary to reach a temperature from 1,000.degree. C. to the melting point of silicon on a certain spot, typically 1 cm in diameter. This annealing is carried out in ambient air while the sample is moved along a spiral at a constant speed. We consider, however, that in this setup, the wafer is still heated as a whole from the back side by the plurality of lamps, which leads to rediffusion of a previously implanted impurity.